commit 4fad66fbe637818b6b3d6bc5d21923ba72795040
Author: James McCoy <jamessan@jamessan.com>
Date:   Sun Nov 20 08:42:38 2016 -0700

    vim-patch:8.0.0056
    
    Problem:    When setting 'filetype' there is no check for a valid name.
    Solution:   Only allow valid characters in 'filetype', 'syntax' and 'keymap'.
    
    https://github.com/vim/vim/commit/d0b5138ba4bccff8a744c99836041ef6322ed39a

diff --git a/src/nvim/option.c b/src/nvim/option.c
index 0f95974..469aeec 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -2399,6 +2399,18 @@ static char *set_string_option(const int opt_idx, const char *const value,
   return r;
 }
 
+/// Return true if "val" is a valid 'filetype' name.
+/// Also used for 'syntax' and 'keymap'.
+static bool valid_filetype(char_u *val)
+{
+  for (char_u *s = val; *s != NUL; s++) {
+    if (!ASCII_ISALNUM(*s) && vim_strchr((char_u *)".-_", *s) == NULL) {
+      return false;
+    }
+  }
+  return true;
+}
+
 /*
  * Handle string options that need some action to perform when changed.
  * Returns NULL for success, or an error message for an error.
@@ -2623,8 +2635,12 @@ did_set_string_option (
     xfree(p_penc);
     p_penc = p;
   } else if (varp == &curbuf->b_p_keymap) {
-    /* load or unload key mapping tables */
-    errmsg = keymap_init();
+    if (!valid_filetype(*varp)) {
+      errmsg = e_invarg;
+    } else {
+      // load or unload key mapping tables
+      errmsg = keymap_init();
+    }
 
     if (errmsg == NULL) {
       if (*curbuf->b_p_keymap != NUL) {
@@ -3118,8 +3134,16 @@ did_set_string_option (
       if (check_opt_strings(p_icm, p_icm_values, false) != OK) {
         errmsg = e_invarg;
       }
-  // Options that are a list of flags.
+  } else if (gvarp == &p_ft) {
+    if (!valid_filetype(*varp)) {
+      errmsg = e_invarg;
+    }
+  } else if (gvarp == &p_syn) {
+    if (!valid_filetype(*varp)) {
+      errmsg = e_invarg;
+    }
   } else {
+    // Options that are a list of flags.
     p = NULL;
     if (varp == &p_ww)
       p = (char_u *)WW_ALL;
diff --git a/src/nvim/testdir/test_options.vim b/src/nvim/testdir/test_options.vim
index cceb180..93657f8 100644
--- a/src/nvim/testdir/test_options.vim
+++ b/src/nvim/testdir/test_options.vim
@@ -38,3 +38,53 @@ function! Test_path_keep_commas()
 
   set path&
 endfunction
+
+func Test_filetype_valid()
+  set ft=valid_name
+  call assert_equal("valid_name", &filetype)
+  set ft=valid-name
+  call assert_equal("valid-name", &filetype)
+
+  call assert_fails(":set ft=wrong;name", "E474:")
+  call assert_fails(":set ft=wrong\\\\name", "E474:")
+  call assert_fails(":set ft=wrong\\|name", "E474:")
+  call assert_fails(":set ft=wrong/name", "E474:")
+  call assert_fails(":set ft=wrong\\\nname", "E474:")
+  call assert_equal("valid-name", &filetype)
+
+  exe "set ft=trunc\x00name"
+  call assert_equal("trunc", &filetype)
+endfunc
+
+func Test_syntax_valid()
+  set syn=valid_name
+  call assert_equal("valid_name", &syntax)
+  set syn=valid-name
+  call assert_equal("valid-name", &syntax)
+
+  call assert_fails(":set syn=wrong;name", "E474:")
+  call assert_fails(":set syn=wrong\\\\name", "E474:")
+  call assert_fails(":set syn=wrong\\|name", "E474:")
+  call assert_fails(":set syn=wrong/name", "E474:")
+  call assert_fails(":set syn=wrong\\\nname", "E474:")
+  call assert_equal("valid-name", &syntax)
+
+  exe "set syn=trunc\x00name"
+  call assert_equal("trunc", &syntax)
+endfunc
+
+func Test_keymap_valid()
+  call assert_fails(":set kmp=valid_name", "E544:")
+  call assert_fails(":set kmp=valid_name", "valid_name")
+  call assert_fails(":set kmp=valid-name", "E544:")
+  call assert_fails(":set kmp=valid-name", "valid-name")
+
+  call assert_fails(":set kmp=wrong;name", "E474:")
+  call assert_fails(":set kmp=wrong\\\\name", "E474:")
+  call assert_fails(":set kmp=wrong\\|name", "E474:")
+  call assert_fails(":set kmp=wrong/name", "E474:")
+  call assert_fails(":set kmp=wrong\\\nname", "E474:")
+
+  call assert_fails(":set kmp=trunc\x00name", "E544:")
+  call assert_fails(":set kmp=trunc\x00name", "trunc")
+endfunc